Lecture 12-Chapter 20-Galaxies

Chapter 20 Galaxies The 3 Major Types of Galaxies N Spiral Galaxies: Like our Milky Way, look like flat white disks with yellowish bulges at their centers. N Elliptical Galaxies: are redder, more rounded, and often longer in one direction than in the other two. Contain less cool gas or dust, but contain very hot, ionized gas. N Irregular Galaxies: appear neither disklike nor rounded. N The differing colours of galaxies arise from the different kinds of stars that populate them. N Galaxies come in different sizes, from white dwarf galaxies containing as few as 100 million stars to giant galaxies with more than 1 trillion stars. Spiral Galaxies N There are two primary components of galaxies: N The disk component is the flat disk in which stars follow orderly, nearly circular orbits around the galactic center. N Always contains an interstellar medium of gas and dust. Galaxies with large bulges have less interstellar gas and dust than those with small bulges. N The spheroidal component contains the bulge and the halo. N Have orbits with many different inclinations, and contains little cool gas or dust. N Some spiral galaxies appear to have a straight bar of stars cutting across the center, with spiral arms curling away from the ends of the bar, these galaxies are known as barred spiral galaxies. N Other galaxies have disk and spheroidal components like spiral galaxies but appear to lack spiral arms, these galaxies are called lenticular galaxies, containing less cool gas than normal spirals but more than ellipticals. Elliptical Galaxies N Elliptical galaxies lack a significant disk component. N Has only a spheroidal component and looks much like the bulge and halo of a spiral galaxy. N Come in wide range of sizes. N Although most galaxies are spiral, some of the most massive galaxies are giant elliptical galaxies. N Small ellipticals, dwarf elliptical galaxies, are often found near larger spiral galaxies. N Usually contain very little dust or cool gas N Large elliptical galaxies can contain substantial amounts of very hot gas. N The lack of cool gas in elliptical galaxies means that they generally have little or no ongoing star formation. N Thus, elliptical galaxies tend to look red or yellow, because they do not have any of the hot, young, blue stars found in the disks of spiral galaxies. Irregular Galaxies N This irregular class of galaxies is a miscellaneous class, encompassing small galaxies 8:.K,8,J0OO,3L.O4:8,3O,7J0750.:OL,7J,O,[L089K,9,550,794-0L3L8,77, N These blobby star systems are usually white and dusty, like disks of spirals. www.notesolution.com